Gasoline producing process



oct. 27, 1970 ,Q SWE ETAL 3,536,609

GASOLINE PRODUC ING PROCES S Filed Nov. 5, 1967 Laurence 0. Stine By Jac/r B. Pah/enz ATTORNEYS United States Patent O U.S. Cl. 208-72 6 Claims ABSTRACT F THE DISCLOSURE Process for the enhanced production of high octane gasoline in a catalytic cracking process wherein a hydrocarbonaceous feed oil and a recycled heavy cycle oil are catalytically cracked in a first dilute phase riser reaction zone, a recycled hydrotreated light cycle oil is at least in part separately catalytically cracked in a second dilute phase riser reaction zone, the weight ratio of catalyst to oil entering the first reaction zone being greater than the weight ratio of catalyst to oil in the second reaction zone, and the catalytically cracked hydrotreated light cycle oil is employed to strip hydrocarbonaceous material off partially deactivated catalyst in a dense phase reaction zone.

This invention relates to the production of high octane gasoline. More specifically, this invention relates to the production of gasoline from heavy hydrocarbonaceous feeds by a route which results higher octane number and higher yields. Still more specifically, this invention relates to the upgrading of a normally refractory byproduct stream from a catalytic cracker such that it may be converted to gasoline of high quality `under catalytic cracking conditions especially selected to optimize the conversion of this stream. Furthermore, this invention relates to a I-factor analysis of the upgrading step to correlate this analysis with catalytic cracking conversion conditions to optimize the yield and octane improvement attained when the upgraded byproduct stream is converted to gasoline.

In one of its embodiments, this invention relates to a procees for producing high octane gasoline from heavier oil which comprises the steps: (a) catalytically cracking a heavy hydrocarbonaceous feed oil and a heavy cycl oil as defined in step (e) hereinbelow in a rst catalytic cracking zone maintained at catalytic cracking conditions and containing a cracking catalyst; (b) catalytically cracking a hydrotreated light cycle oil as defined in step (g) hereinbelow in a second catalytic cracking zone maintained at catalytic cracking conditions and containing a cracking catalyst, the catalyst to oil weight ratio entering the first catalytic cracking zone being greater than the catalyst to oil weight ratio entering the second catalytic cracking zone; (c) withdrawing a product from the catalytic cracking zones and introducing said product into separation zone; (d) recovering a high octane gasoline from the separation Zone; (e) recovering heavy cycle oil from the separation zone and returning said heavy cycle oil to step (a), (f) recovering a light cycle oil having an average boiling point above the average boiling point of the gasoline of step (d) and below the average boiling point `of step (e), said light cycle oil being rich in aromatics, the major type being J-12; (g) hydrotreating at least a portion of the light cycle oil of step (f) by contacting said light cycle oil with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions in a reaction zone to retain a major portion of the aromatics and convert the types of aromatics such that the major type is J-8 and withdrawing a hydrotreated light cycle oil from the reaction zone; and (h) returning at least a portion of the hydrotreated light cycle oil to step (b).

In another of its embodiments, this invention relates to an improvement in a process for the production of gasoline wherein a feed oil and a hydrotreated cycle oil are catalytically cracked in a catalytic cracking reaction zone, said improvement comprising separately cracking 4the feed oil in a lirst cracking reaction zone and the hydrotreated cycle oil in a second cracking reaction zone, the entering weight ratio of cracking catalyst to oil being greater in the first reaction zone than in the second reaction zone.

It has been known for many years that heavy feed oils such as gas oil, vacuum gas oil, coke gas oils, etc., may be cracked in the presence of a cracking catalyst to produce light hydrocarbons (C4 minus which are rich in olens) and high octane gasoline (C5 plus to about 430 F. end point which is recovered as primary product). In addition, most catalytic crackers must be operated at conditions such that an oil heavier than gasoline is produced from the reaction zone. The reaction products from the catalytic cracking reaction zone are introduced into a fractionator and separated therein. Typically, the fractionator has an upper side cut well and a lower side cut well and is operated to remove gasoline and light hydrocarbons overhead, a heavy cycle oil from the lower side cut well (material produced from the lower well maintained at about 550 F.), a bottoms or slurry oil (material produced yfrom the column bottoms maintained at about 700 F.) and a refractory light cycle oil from the upper side cut well (material produced from the upper well maintained at about 440 F.). Generally, the heavy cycle oil is recycled to the catalytic cracking zone while the slurry oil is clarified whereupon it may be cracked or recovered as a fuel oil. The refractory light cycle oil generally is not recycled to the catalytic cracking zone since it is refractory and not as readily crackable in comparison to the feed stock and the heavy cycle oil. It is also been taught to hydrogenate this refractory oil to irnprove its cracking characteristics. For example, U.S. Pat. 2,671,754 shows the separate desulfurization and hydrogenation of this refractory oil. Other articles have shown general improvement in crack-ing characteristics of cycle oils by hydrogenation as, for example, shown in the Chemistry of Petroleum Hydrocarbons, volume 3 Chapter 52, pages 333 to 334. However, the prior art -has failed to recognize the ultimate improvement in high quality gasoline obtained therefrom, the manner in which the hydrogenation should be carried out, to optimize the gasoline producing process and the conditions under which the hydrotreated oil should be catalytically cracked `in order to optimize the gasoline producing reaction in terms of yield and octane number. The present invention provides for the hydrotreating of the light cycle oil in a specific manner and the subsequent cracking of said light hydrotreated cycle oil under particular conditions to optimize its conversion to gasoline.

An analytical technique has been developed which permits the characterization of various types of aromatics in a hydrocarbon mixture called a I-factor analysis. It is in esseince a mass spectrometer analysis employing a low ionizing voltage technique. The ionizing chamber is maintained at a potential of about 7 volts and the vaporized hydrocarbon mixture is introduced therein. Compounds more saturated than aromatics such as parafins have an ionization potential above 10 volts and these saturated compounds will not be observed on the mass spectrum since they are not ionized. The mass spectrum reveals molecular ion peaks which correspond to the molecular weight of the aromatic compound which permits characterization of these aromatics by means of the gen- ICC eral formula: CnH2n J where I is the J-factor. The following table shows the releationships between the J-factor and the type of aromatic.

TABLE I Type of aromatic J -Factor hydrocarbon numb er Alkyl benzenes and benzene 6 Indanes and tetralins 8 Indenes Alkyl naphthalenes and naphthalene 12 Acenaphthenes, tetrahydroanthracenes 14 Accnaphthalenes, dihydroanthracenes 16 Anthracenes, phenanthrenes 18 Using this .l-factor analysis in characterizing the hydrotreating step of this invention allows for the optimum treatment of said refractory oil to produce a high quality gasoline by subsequent catalytic cracking of the hydrotreated oil. It must be borne in mind that there is a relationship between the hydrotreating step and the subsequent catalytic cracking rstep such that the light cycle oil is hydrotreated to the proper extent and then catalytically cracked to the proper extent. Under the appropriate circumstances, the present invention allows the complete conversion of the refractory light cycle oil into high quantity gasoline.

It is an object of this invention to render a light cycle oil derived from a catalytic cracker readily susceptible to further cracking.

It is another object of this invention to hydrotreat a refractory cycle oil derived from a first catalytic cracking zone and thereafter contact the hydrotreated cycle oil with a catalytic cracking catalyst in a second catalytic cracking zone, the weight ratio or cracking catalyst to oil entering the iirst zone being greater than said ratio entering the second zone.

It is a more specific object of this invention to separately catalytically crack a hydrotreated cycle oil derived from a fresh feed oil catalytic cracking zone and a fresh feed oil using common regeneration facilities to regenerate cracking catalyst.

These and other objects will become more apparent in the light of the following detailed description.

The accompanying drawing shows a schematic flow scheme for one preferable embodiment of the present invention in which separate catalytic cracking ones are employed to crack (a) the hydrotreated light cycle oil and (b) the fresh feed stock and the recycled heavy cycle oil. As shown in the igure, a feed stock is introduced into conduit 1 where it is commingled with recycled heavy cycle oil flowing in conduit 2 and the resulting mixture ows into conduit 3a` whereupon it mixes with hot regenerated cracking catalyst flowing in conduit 4. The feed stock, heavy cycle oil and catalyst are mixed therein and flow upward through dilute phase riser 5 and into cyclone 7 contained within reaction chamber 6. The catalyst is composed of fine particles such that it acts as a fluid bed. Therefore, the catalyst will flow down through conduit 4 under the influence of gravity and will ow up coeurrently along with the feed stock and heavy cycle oil through conduit 5 in a dilute phase wherein the cracking reactions occur. The fresh feed and heavy cycle oil react in conduit 5 under the catalytic inlluence of the cracking catalyst to produce a wide variety of products including light hydrocarbons, gasoline, refractory light cycle oil, heavy cycle oil, slurry oil and coke. The coke generally is formed on the fluid catalyst particles. The catalyst is separated from the reaction products by settling and by means of cyclone 7. Although the schematic flow scheme shows one cyclone it is contemplated that a bundle of parallel and/ or series ow cyclones may be employed to attain an eicient separation between the reaction products and the catalyst. The reaction products pass through cyclone 7 and into cyclone 9 where they orw' through conduit 11 and out of reaction chamber 6. These reaction products ilow through conduit 11 and into fractionator 12. A hydrocarbon stream containing light hydrocarbons and gasoline is withdrawn overhead from fractionator 12 through conduit 13 where is ows through cooler 14 and into separator 40. Vapor phase light hydrocarbons composed mainly of C1 to C4 hydrocarbons are withdrawn from separator 40 through conduit `41. Liquid phase gasoline is withdrawn from separator `40 through conduit 42 fwhereupon it is recovered as the desired principal product of the process. Heavy cycle oil is withdrawn from fractionator 12 through conduit 2 where it is returned to conduit 3 being mixed therein with feed stock. Slurry oil is withdrawn from the bottom of fractionator 12 through conduit 25 where it is introduced into settler 26. The claritied slurry oil is withdrawn through conduit 27 where it may be used as a fuel oil or it may be recycled back to flow conduit 2.3 for further cracking and conversion.

A refractory light cycle oil is withdrawn from fractionator 12 through conduit 15 where it flows through conduit 16 and into hydrotreating reaction zone 18. Hydrogen from a source delined hereinafter flows through conduit 17 and is commingled with the refractory light cycle oil and the mixture flows through conduit 16. The hydrotreating step is preferably carried out by loading the hydrotreating catalyst into a fixed bed within zone 18. The material to be hydrotreated passes through the fixed bed of catalyst maintained at hydrotreating conditions. An eluent is withdrawn from reaction zone 18 through conduit 19 which is cooled and introduced into separator 20. The effluent is separated into a normally liquid hydrotreated product and a normally gaseous stream. The normally gaseous stream is Withdrawn from separator 20 through conduit 21 where it flows through recycle compressor 22 and through conduit 23 where it is commingled with fresh hydrogen ilowing in conduit 24 and the combined hydrogen gaseous stream material then ilows through conduit 17, conduit 16 and back to reaction zone 18. lf desired, a portion of the normally gaseous stream may be vented to maintain hydrogen purity although this is not generally necessary. The normally liquid product stream is withdrawn from separator 20 through conduit 28 where if desired it may be flashed or stripped to remove dissolved gases such as hydrogen and hydrogen sulfide although this step may be omitted. In some instances, a portion of this oil is used as a hydrotreated fuel oil, in which case it may be withdrawn through conduit 35 by opening valve 36. The hydrotreated light cycle oil is returned to the catalytic cracking zone through conduit 28 where it mixes with hot regenerated catalyst iiowing in conduit 29 and the mixture flows concurrently through dilute phase riser 30 and into reaction zone chamber 6. The hydrotreated light cycle oil is cracked to lighter products in riser 30, and such lighter products are elective in stripping heavier hydrocarbonaceous materials off the catalyst contained within the dense bed in the lower portion of reaction zone 6. The cracked hydrotreated light cycle oil reaction products flow into cyclone 9 to separate any entrained catalyst from the reaction products and the products are commingled With the reaction products of the fresh feed and heavy cycle to produce a total effluent leaving conduit 11 as described hereinbefore. Cyclone 7 and 9 may contain diplegs 8 and 10 respectively to seal the cyclone bottom to the dense -bed of catalyst. lf additional outside charge stock is available which is refractory in nature, it may be introduced into this ilow scheme through conduit 37 where it mixes with the refractory light cycle oil prior to entering the hydrotreating reaction zone. Generally charge stock would only be introduced at this point because it is diicult to catalytically crack relative to the feed stock and the heavy cycle oil. In this event this outside charge stock is hydrotreated to render it more easily crackable while optimizing the J-factor treatment of said stock to optimize the subsequent conversion thereof in the catalytic cracking zone to produce high quality gasoline in high yields therefrom.

The fluid cracking catalyst introduced into reaction chamber 6 via risers 5 and 30 are commingled and withdrawn from a lower portion of chamber 6 and introduced into stripper 31. Generally, steam is introduced into stripper 31 through conduit 38 where it countercurrently contacts the descending liuidized partially deactivated cracking catalyst to strip entrained oil off the catalyst. The partially deactivated catalyst has been contacted with the cracked hydrotreated light cycle oil in the dense bed above Stripper 31, which results in its effective stripping of such partially deactivated catalyst to remove heavier components which reduces the required stripping steam. As a result of this flow scheme, it has been found that the steam required to strip the remaining entrained oil olf the decending catalyst through the stripper is markedly reduced. It should be recognized that the catalyst contained Within chamber 6 has been partially deactivated due to the conversion reactions that have occurred over it With the deposition of coke thereon. This catalyst in a partially deactivated form is carried back into the regenerator vessel in order to reactivate the catalyst by burning a portion of the coke thereoff. The liuid partially deactivated catalyst passes through stripper 31 and enters regenerator charnber 32. Air is introduced into regenerator chamber 32 through conduit 33 where the oxygen contained therein reacts with a portion of the coke on the catalyst to produce carbon oxides. An efuent gas comprising nitrogen and carbon oxides is Withdrawn from regenerator chamber 32 through conduit 34. The catalyst that has now been regenerated contained within regenerator vessel 32 is withdrawn therefrom through either conduit 29 or 4 to begin the cycle over again.

It should be noticed that the hydrotreated light cycle oil contacts catalysts in riser 30 and also a dense bed of partially deactivated catalyst in chamber 6. This flow scheme is used in order to reduce or eliminate the need for extra catalyst circulation as a result of cracking the light cycle oil into the gasoline boiling range.

The principal reaction that occurs in zone 18 is the conversion of L12 type aromatics to 1 8 type aromatics. Over-hydrogenation will either saturate the aromatic ring to produce non-aromatic hydrocarbons or will result in hydrocracking of the side-chain I-S to produce a 1 6 aromatic hydrocarbon. Neither of these reactions are desired since they consume too much hydrogen. It has been found that upon proper hydrogenation of the light cycle oil to maximize its J-S content, this material is readily cracked in riser 30 wherein the ratio of the weight ratio of cracking catalyst to oil is less than the Weight ratio of cracking catalyst to oil in riser 5. This will reduce the need for additional circulation as Well as reduce the required stripping steam.

It is to be understood, of course, that there are numerous variations in the basic catalytic cracking process in terms of fluidized bed, xed beds, etc., and it is intended that all of the basic catalytic cracking processing schemes be included in the process of the present invention.

Other ow schemes may be practiced besides that shown in the accompanying drawing which may be used to take advantage of the processing scheme of the present invention. Conversions to gasoline of up to 100% are also possible. One basic variation is to eliminate the heavy cycle oil stream. This may be done by a combination of hydrotreating the total cycle oil fraction and/or increasing the catalytic cracking severity. In this manner no material would be owing in conduit 2 in the drawing. Therefore, the entire cycle oil stream would be hydrotreated to upgrade its crackability.

There are a large number of catalysts suitable for use in the catalytic cracking step such as amorphous silicaalumina, silica-magnesia, silica-zirconia, acid-activated clay, crystalline catalysts including faujasite dispersed in a silica-containing inorganic oxide matrix, mordenitecontaining catalysts either dispersed in a silica-containing matrix, or an alumina-containing matrix or used in the pure form, etc. Preferred cracking catalysts for use in the present process are `amorphous silica-alumina having concentrations of from to about 40 weights of alumina and 90 to about 60 weights of silica and faujasite dispersed in a silica-containing inorganic oxide matrix especially from about 2 to about 20% faujasite in a silica or silica-alumina matrix. Other suitable ingredients may be added to the faujasite dispersed matrix catalyst such as hydrogen cations, rare earth cations and other polyvalent cations to take the place of the sodium ions present in the faujasite structure. Typical catalytic cracking operation conditions comprise reactor temperatures of from about 800 F. up to about 1050" F., regenerator temperatures of from about 1000 F. to about 1300" F., pressures of from about atmospheric to about 50 p.s.i.g., oil to catalyst weight ratios of from about 1.0 to about 10.0 and combined feed ratio (ratios of fresh feed plus heavy cycle oil divided by fresh feed) of from about 1.1 to about 2.0. These variables, some of which are independent and some of which are dependent, are adjusted to maintain conversions per pass to gasoline of from about 30% up to about 70% and in some instances up to about The hydrotreating catalyst is preferably sulfur resistant, that is it possesses hydrogenation activity in the presence of sulfur compounds. A preferable catalyst cornprises a silica-alumina support having at least one metal or metal compound of Group VI of the Periodic Table and one metal or metal compounds of Group VIII of the Periodic Table. Especially preferable are those catalysts having tungsten and/or molybdenum along with nickel and/or cobalt on silica-alumina supports. Other supports such as alumina, silica-zirconia, silica-magnesia, faujasite, mordenite, inorganic oxide matrix containing at least one crystalline aluminosilicate, etc., are `also suitable. Other metals besides the ones described hereinabove are also suitable as for example noble metals such as platinum or palladium. These latter catalysts are generally satisfactory without the presence of a Group Vl metal.

The hydrotreating conditions employed in hydrotreater 18 such as temperature, pressure, LHSV, hydrogen to oil ratio, etc., are selected to convert the refractory light cycle oil or cycle oil to a product having as the major type of aromatic hydrocarbon J-S as dened hereinbefore. It has been found that the refractory light cycle oils have J-12 as the major single type of aromatic hydrocarbon. Therefore, the above hydrotreating process v-ariables are controlled to maximize ythe J-12 to J-8 conversion reaction. It is generally preferable to maintain pressure, LHSV and hydrogen to oil constant and vary temperature to maximize the 1 12 to I-S conversion. The initial choice of al1 these variables depends to `a large measure on the charge stock. Suitable pressure ranges are from about 400 up to about 2000 p.s.i.g. with 600 to 1200 being preferable. Suitable LHSV is from about 0.5 to about 20, with 3 to 10 being preferable. Suitable hydrogen to oil -rnole ratios of from about 2 to about 20 with 5 to 15 being preferable. When these conditions are selected, the temperature is adjusted to maximize the J-l2 to I-S conversion. It is expected that temperatures Within the range of about 500 F. to about 850 F. will be employed. The most preferred Way to attain the proper operating conditions is to select the independent variables, conduct a J-factor analysis on the stream flowing in conduit 15 and 28 and adjust temperature to attain the maximum conversion of J-12 to 1 8. If the operating conditions are too severe, the J-12 will be converted to J-6 or the aromatics will be saturated. This has the undesirable effect of increasing hydrogen consumption in the hydrotreater and reducing the octane number of the gasoline when the hydrotreated light cycle is subsequently catalytically cracked. If the hydrotreatng conditions are not severe enough, there will be little improvement in the refractory nature of the light cycle oil which will make it ditlicult to convert to gasoline. When properly hydrotreated, this material is readily catalytically cracked -according to the process of this invention.

In order to obtain high quality gasolines at conversions 7 of 100%, the hydrotreating conditions may have to be adjusted to account for a foreign charge stock which may be introduced into conduit 37. The nature of this foreign charge stock in contrast to the nature of the refractory light cycle oil will have to be considered in the selection of the nal variables to be employed in hydrotreater 13. It has been found that when the hydrotreated light cycle oil has been catalytically cracked according to the process of the present invention, a gasoline will be produced having 1 6 as the major single type of aromatic present therein, a preferable motor fuel.

It has also been found that the unconverted hydrotreated light cycle oil which has been catalytically cracked (unconverted being defined as having a boiling point range above the boiling point range of gasoline) has a J -factor analysis indicating that the major type of aromatic present in this unconverted oil is I-12. This means that the catalytic cracking zone has converted the hydrotreated light cycle oil boiling above gasoline in conduit 28 having I-S as the major aromatic type into a gasoline having 1 6 as the major aromatic type and a material boiling above gasoline having J-12 as the major aromatic type. For this reason, any unconverted hydrotreated light cycle oil will be readily recycled and cracked to extinction by recycling it back through the hydrotreating step again since the J-12s are then reconverted to J-Ss. This will allow the complete conversion of the light cycle oil into gasoline boiling range material or lighter.

It is now apparent that the present invention permits the conversion of gas oil feed stocks to gasoline and lighter in amounts of 90% or higher. Indeed, conversions of up to 100% are possible with the process of this irivention providing the slurry oil is also cracked. ln this sense, this overall process has the same advantages as hydrocracking to produce gasoline from gas oils, a feat which up until now has been impossible. Furthermore, the light hydrocarbons produced in conduit 41 are rich in olens which permits alkylation with paraflins to produce high octane isoparans which can be added to the total gasoline yield. When this is practiced, the present process in combination with alkylation will produce a most desirable high octane motor fuel having as its main components, alkylbenzene aromatics and isoparains. Another advantage is that the catalytic cracking and the hydrotreating step are carried out at relatively low pressures when compared to hydrocracking thus minimizing capital investment and operational problems.

It is diflicult to characterize the split points between the light refractory cycle oil and the gasoline and heavy cycle oil by commonly observed physical characteristics since this split point varies depending upon the initial feed stock, operating conditions, and desired yields, etc. In some cases, the end point of the light cycle oil will vary from about 550 F. or less to as much as 750 F. or more. The most preferable manner of characterizing the light cycle oil and the heavy cycle oil is the place from which each originates. As used herein, heavy cycle oil is that material Withdrawn from the lower side cut well in the catalytic cracking main column fractionator, said well being maintained at about 550 F. The gasoline from the catalytic cracker may be characterized by the boiling point range or end point, the end point generally being within the range of from about 350 F. up to about 450 F. and typically about 430 F. The light refractory oil is the material boiling between the gasoline and the heavy cycle oil. The light refractory cycle oil is derived from an upper side cut well in the main column fractionator 12 said Well being maintained at about 440 F. The side cut well temperatures are for fractionator pressures of about to about 15 p.s.i.g. and if the pressure is outside this range, the well temperatures will, of course, be shifted. Suitable feed stocks for introduction into conduit 1 comprise gas oils such as ordinary gas oil, vacuum gas oil, coker gas oil, etc. Suitable charge stocks for introduction into conduit 37 are those hydrocarbonaceous feeds derived from other sources which are more diicult to catalytically crack than the feed stock material. Sources of such outside charge stocks for introduction into conduit 37 would be cycle oils from other catalytic cracking operations, purchase cycle oils, etc.

It is also within the scope of this invention to vary the relative diameters of riser 5 and riser 30 to attain more or less slippage in the respective risers to optimize the conversion of the feed stock heavy cycle oil mixture in relationship to the hydrotreated light cycle oil.

The following example is presented to further illustrate the process of the present invention.

EXAMPLE Equipment is arranged substantially as shown in the accompanying drawing. A mixture of atmospheric and vacuum gas oil is introduced into the catalytic cracking reaction zone through conduit 1. The reactor zone is maintained at temperatures of about 900 F. and pressures of 19 p.s.i.g. The combined feed ratio is about 1.2. A refractory light cycle oil is withdrawn from conduit 15 from fractionator 12 in an amount of about 20% of the volume of fresh feed where it flows into hydrotreater 18. The hydrotreater is maintained at a pressure of about 800 p.s.i.g., a liquid hourly space velocity of about 2, the hydrogen circulation rate of about 3000 s.c.f./bbl. and a temperature of about 700 F. The entire normally liquid product from the hydrotreater is recycled back through conduit 28 into reaction chamber 6 via riser 30. It is estimated that the contact time with which the hydrotreated light cycle oil contacts the catalyst is about twice that of the fresh feed and heavy cycle oil Contact time. It is estimated that the above unit will produce conversions in excess of We claim as our invention:

1. A process for producing high octane gasoline from heavier oil which comprises the steps of:

(a) catalytically cracking a mixture of a hydrocarbonaceous feed oil and a heavy cycle oil as defined in step (f) below by contacting said mixture at cracking conditions with iluidized cracking catalyst in a first dilute phase upiiow riser cracking zone;

(b) separating the reaction product of step (a) from the cracking catalyst and passing the separated catalyst into a dense phase uidized bed of cracking catalyst;

(c) catalytically cracking a hydrotreated light cycle oil as defined in step (h) below by contacting said hydrotreated light cycle oil at cracking conditions with iuidized cracking catalyst in a second dilute phase upflow riser cracking zone which is independent of said first riser cracking zone, and thereafter introducing the eiuent from said second riser cracking zone into said dense phase bed of cracking catalyst to strip heavy hydrocarbonaceous material from the catalyst;

(d) recovering the reaction product of step (c) and introducing it, together with the reaction product of step (a), into a separation zone;

(e) recovering a high octane gasoline from said separatlon zone;

(f) recovering heavy cycle oil from said separation zone and returning said heavy cycle oil to step (a);

(g) recovering from said separation zone a light cycle oil having an average boiling point above the average boiling point of the gasoline of step (e) and below the average boiling point of the heavy cycle oil of step (f), said light cycle oil being rich in aromatics, the major type being 1 12;

(h) hydrotreating at least a portion of the light cycle oil of step (g) by contacting said light cycle oil with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions selected to retain a major portion of the aromatics and to convert the aromatics mainly to type 1 8; and

(i) returning at least a portion of the resulting hydrotreated light cycle oil to step (c).

2. The process of claim 1 further characterized in that the catalyst to oil weight ratio of the mixture entering said rst riser cracking zone is greater than the catalyst to oil weight ratio of the charge entering said second riser cracking zone.

3. The process of claim 2 further characterized in that the total amount of hydrotreated light cycle oil obtained from step (h) is returned to said second riser cracking zone.

4. A process for producing high octane gasoline from heavier oil which comprises the steps of:

(a) catalytically cracking a heavy hydrocarbonaceous feed oil by contacting said feed oil at cracking conditions with iluidized cracking catalyst in a rst dilute phase upow riser cracking zone;

(b) separating the reaction product of step (a) from the cracking catalyst and passing the separated catalyst into a dense phase uidized bed of cracking catalyst;

(c) catalytically cracking a hydrotreated light cycle oil as dened in step (g) below by contacting said hydrotreated light cycle oil with fluidized cracking catalyst in a second dilute phase upflow riser cracking zone which is independent of said iirst riser cracking zone, and thereafter introducing the eluent from said second riser cracking zone into said dense phase bed of cracking catalyst to strip heavy hydrocarbonaceous material from the catalyst;

Id) recovering the reaction product of. step (c) and introducing it, together with the reaction product of step (a), into a separation zone;

(e) recovering a high octane gasoline from said separation zone;

(f) recovering from said separation zone a light cycle oil having an average boiling point above the average boiling point of the gasoline of step (e), said light cycle oil being rich in aromatics, the major type being J-12;

(g) hydrotreating at least a portion of the light cycle oil of step (f) by contacting said light cycle oil with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions selected to retain a major portion of the aromatics and to convert the aromatics mainly to type 1 8; and

(h) returning at least a portion of the resulting hydrotreated light cycle oil to step (c).

5. The process of claim 4 further characterized in that the catalyst to oil Weight ratio of the charge entering said rst riser cracking zone is greater than the catalyst to oil weight ratio of the charge entering said second riser cracking zone.

6. The process of claim 4 further characterized in that partially deactivated catalyst is Withdrawn from said dense phase bed, subjected to regeneration, and the resulting regenerated catalyst is returned in separate streams to said first and second riser cracking zones, respectively.

References Cited UNITED STATES PATENTS 3,065,166 11/1962 Hennig 208-67 DELBERT E. GANTZ, Primary Examiner A. RIMENS, Assistant Examiner U.S. Cl. X.R. 208- 

